charging issue

Discussion in 'Airheads' started by mslim, Jul 1, 2020.

  1. mslim

    mslim If it's worth doing... it's worth overdoing

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    I am attempting to troubleshoot an intermittent charging issue on my 75 R90S with the stock Bosch alternator. I had seen a flickering GEN light at road rpm. I thought I'd first test the regulator as described below:

    REGULATOR TESTS:
    In case the Regulator is faulty and preventing the Alternator from charging, perform the following tests:

    TEST 1H:
    1. Disconnect the D+ and DF wires from the Regulator and join these wires temporarily together so as to bypass the Regulator completely.
    NOTE: Check the wiring at the Regulator connector for corrosion or overheating - gently pull the wires to check they are secure.
    2. Start the engine and see if the Charge light goes out - if so, the Regulator is likely faulty.


    When I turned on the key I didn't have the usual GEN light just the Neutral and Oil Pressure.

    I started the bike and revved up to 2000-3000 rpm but no change in the GEN light, it stayed unlit.

    What does this indicate?
    #1
  2. Big Bamboo

    Big Bamboo Aircooled & Sunbaked Supporter

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    Short one of the rotor slip rings to 'earth' - earth being any clean bit of metal on the bike .. an engine cooling fin being one example.
    Check if the alternator warning light comes on or off -don't start the engine just check the light on/off with ignition power on.

    Repeat the above test for the other slip ring.

    Result;

    For the two tests the light came on;

    never - globe faulty, or possibly the wire from the globe to the rotor OR one of the slip ring brushes not making contact
    Once - rotor faulty.
    both times - one faulty brush to slip ring contact OR the 'earth' contact for a brush is faulty

    -----------------------------
    If the rotor is faulty .. you will need a replacement rotor and a 'special tool' to remove it. The special tool is cheap - bit of hardened rod - buy it ... don't attempt to make your own.

    -----------------------------------
    The power to that light also goes to the oil pressure warning light and the ignition system. If both of those are working it is unlikely to be a power supply problem. Rather it is the 'drain' side ... that goes to the rotor (and voltage regulator etc). When the bike is not running the voltage regulator (etc) takes no part in the 'drain' .. it is the rotor (and the wire leading to it and the brushes) that form the 'drain'. Note; credit goes to Warin for this test. I will add; make sure slip rings are clean. Burnish with Scotchbrite pad with engine running. Also check condition of brushes.
    #2
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  3. mslim

    mslim If it's worth doing... it's worth overdoing

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    Thanks for the detailed info Big Bamboo, but I wanted to do the easier voltage regulator test first to eliminate it from the chain.

    To do the rotor test, I have to drop my 2 into 1 exhaust, disconnect the battery and pull the front cover. If the regulator proves OK, I've got the rotor removal tool and will run your test to get a handle on the rotor condition. I have a feeling it is working it's way up to a failure.
    #3
  4. Big Bamboo

    Big Bamboo Aircooled & Sunbaked Supporter

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    Before doing anything I load test the battery and inspect the terminals;

    You won't get a proper charging voltage reading if the battery has a bad cell or is deeply discharged.

    If the battery is OK...

    ... I simply swap the regulator with a known good one.
    It's the easiest component to access and swap, and a very common fault.
    For this test, you don't have to install the replacement, you can just plug it in.
    I check the bulb circuit by grounding the blue regulator wire (if the bulb is not working at all)

    Next I go to the rotor, easy to test for open or short without removing anything, and I get to check the brush condition at the same time.

    Next the stator, fast and easy to replace, but RARE failure,
    I've seen a few stators 'test' good, but still cause the light to flicker or glow dimly.
    Takes less than 5 minutes. NOTE: Not all stators are interchangeable.

    Then, without removing or disconnecting anything, I check for power (on the bottom half) and ground (on the top half) of the diode board, and do a visual inspection of all its wires.

    If none of the above fixed it, I can confidently inform the customer that he NEEDS a diode board, and mounts, etc. and give him an exact estimate.
    Total shop time for diagnosis; 20 to 30 minutes

    The reason I leave the diode board for last (IT IS A VERY COMMON failure), is that it's sometimes timely to remove and test.
    Often, the rubber mounts break, then the starter cover, air filter, etc. needs to be removed to replace them.

    The only thing that should preclude readers here from adopting this method may be restricted access to spare parts.
    #4
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  5. Warin

    Warin Retired

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    I'd bet you made a mistake with the 2 wires. Either that or there is something wrong with the wiring.

    The D+ wire should be the warning globe connection to earth, as well as the diode board supply.

    The Df wire should be the rotor - this should be less than 10 ohms to earth.

    Neither of the above two wires will be colored brown!!! If you have used a brown wire then you made a mistake.

    Use a digital multi-meter, with one side connected to earth.
    Separate the D+ from the Df wires.
    With the ignition on, engine not started, measure the voltage on the 2 wires. One should be at near battery voltage (the D+ wire), the other at 0 volts (the Df wire). Now switch the ignition off. Measure the resistance of the Df wire to earth .. should be less than 10 ohms.
    #5
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  6. mslim

    mslim If it's worth doing... it's worth overdoing

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    You were right, I had the wires jumpered wrong. I corrected it and with the regulator now out of the circuit, I started the bike and the GEN light extinguished at about its normal rpm (1200-1500) I did your voltage test directly off the battery terminals to the VOM. Alternator charging output showed a rise consistent with rising rpm. I let it go up to 15+V and throttled back and shut off the bike.

    I pulled the tank and turned on the ignition and kill switch. The DCV on the D+ wire and was 12.17V and the DF measured 0. I set the VOM on my 200 ohm scale (the lowest I have) and got about 79 ohms from the DF female terminal in the plug to earthing on the engine cover. Way more than 10 ohms.
    #6
  7. Warin

    Warin Retired

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    Far too much... there is a problem there.

    Or your meter + leads are crap. Short the leads - connect from one to the other.. the reading should be less than 1 ohm. If that is ok .. then .. the following;

    Check the connection from the spade connector to the wire (at the regulator end). then check the wire is not damaged from there to the engine... after that the engine cover comes off ... sorry. Rotor or brushes probably faulty.
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  8. mslim

    mslim If it's worth doing... it's worth overdoing

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    Meter is newish and shorting the leads I get 0.0 ohms. Not sure about checking the wires. The female spades at the three contact regulator plug I understand, Where should I put the other probe to check continuity?

    Yes no apology necessary. It's time to drop the exhaust and pull the cover off and check the rotor thru the slip rings. Thanks for your patience. I'm an electric (and electronic) dumbass.
    #8
  9. Warin

    Warin Retired

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    All you can do, at this stage, is a visual check - try pulling and pushing the wire gently away from the voltage reg connector - should not move away.
    Same with the wire going to the engine - visual check for kinks, nicks and cuts. Any green growth going on is a warning sign.
    #9
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  10. rob_k

    rob_k n00b

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    If it were me, I'd start by replacing the bulb. I had a problem years ago where the bulb filament was broken but making intermittent contact. Drove me crazy until I put in a new bulb and the problem went away.
    For a flickering gen light, I'd also check for worn brushes. If they get short, the snail spring starts making contact with the side of the plastic brush holder and can't push the brush down properly. In a pinch, you can cut a small hunk of plastic bottle cap and place shims between the brush and the tip of the spring. This buys you some miles until you can replace the brush.
    Finally, if the bulb and brushes were OK, I'd suspect the rotor or a crappy connection. Doesn't sound like a regulator issue to me.
    #10
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  11. mslim

    mslim If it's worth doing... it's worth overdoing

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    Brushes and brush holder are new. Sufficient tension on the snail springs. Katdash replacement so no charging bulb issues. I believe the regulator is probably ok based on Warin's test above. Blue, blue/black, and brown wires into the regulator plug seem sound. No corrosion visible, insulation intact, Deoxit on all metal connector surfaces.

    I'm dropping the exhaust and opening the front cover next to check the rotor if it ever gets cool enough to work in my garage anytime soon.
    #11
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  12. Warin

    Warin Retired

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    Note: Until it is fixed... leave the engine cover off. It will run without it.
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  13. rob_k

    rob_k n00b

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    You might also check the three wire cable running between the stator and diode board. If it's the original, they're under $20 to replace.
    #13
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  14. mslim

    mslim If it's worth doing... it's worth overdoing

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    They were replaced when I replaced the OE diode board with an Omega and solid mounts.
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  15. dave0

    dave0 Been here awhile

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    Brush solder joints?
    Spitballing here.
    #15
  16. rob_k

    rob_k n00b

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    Open rotor is a good bet. It wouldn't hurt though to also see if you're really getting +12V to the brushes. Ground out the +12 brush lead and the Gen light should light up.
    #16
  17. Warin

    Warin Retired

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    Battery voltage was measured on the D+ wire engine stopped. That voltage should only come from the 'Gen light'.

    Df resistance at the voltage reg was measured at 79 ohms. That is too high, and there is no possibility of it being caused by;
    stator leads
    'Gen light'...

    Only thing to do is look at the rotor/brushes and associated bits. But not the stator. Nor the 'Gen light'.
    #17
  18. mslim

    mslim If it's worth doing... it's worth overdoing

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    Good idea but the EME brushes have crimped on flat terminals and aren't soldered like the OE brushes. Also I when I put in the new brush holder and stator plate, I tightened the posts they connect to. I lucked out and got the insulated and grounded the first time, because the alternator charged fine for 250 miles before the intermittent GEN light issue arose.
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  19. Warin

    Warin Retired

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    Arr .. new parts do fail. And some things might be over tightened and fail after 250 miles. You do need to check them, don't assume because they are near new that they are good.
    #19
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  20. JimGregory

    JimGregory Long timer Supporter

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    Wait!
    Did you say you have a cat dash instrument board? So do I. If you put a volt meter to your battery when running, does it indicate all is well? If so just stop all the fussing and call Cat. She will explain.
    Technically speaking, the CATDASH LED indicator light reacts a jillion time quicker then the old filament bulb. When your battery gets up to full power after starting, some mystical electric shit happens, and the indicator light (can) does the flicker thing. Most obvious at night when it shows up well. Let me know.
    As an aside. I just went through a very intermittent charging issue when the bike was hot. Rather then test everything with my meter and a heat gun, I just bought the EME, basic entire system, and replaced everything. 200 bucks later all is well. Most likely it was my old diode board but whatever. Now everything is solid. I run all LED lighting and really don't need more then 180 watts, in case you are wondering why I didn't spend more and get more wattage. A healthy 180 watts is plenty.
    #20
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